<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box {
            display: flex
        }
        .a {
            width: 100px;
            height: 100px;
            background-color: #6593ee
        }
        .b {
            flex: 1;
            background-color: #ea48c4
        }

    </style>
</head>
<body>
    <div class="box">
        <div class="a"></div>
        <div class="b"></div>
    </div>
</body>
</html>
